diff for file comparison in Linux CLI - Step-by-Step Execution

Concept Flow - diff for file comparison

Start: Two files

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Run diff command

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Compare lines one by one

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Detect differences

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Show output with line numbers and change symbols

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End

The diff command compares two files line by line and shows where they differ.

Execution Sample

Linux CLI

diff file1.txt file2.txt

Compares file1.txt and file2.txt and shows their differences.

Execution Table

Step	Action	File1 Line	File2 Line	Difference Detected	Output
1	Read line 1	Hello world	Hello world	No
2	Read line 2	This is line two	This is line 2	Yes	2c2 < This is line two --- > This is line 2
3	Read line 3	End of file	End of file	No
4	End of files				Comparison complete

💡 Reached end of both files, diff output shows all differences found.

Variable Tracker

Variable	Start	After Step 1	After Step 2	After Step 3	Final
line_number	0	1	2	3	3
difference_found	false	false	true	true	true
output	""	""	2c2 < This is line two --- > This is line 2	2c2 < This is line two --- > This is line 2	2c2 < This is line two --- > This is line 2

Key Moments - 2 Insights

Why does diff show '2c2' in the output?

The '2c2' means line 2 in file1 is changed ('c') compared to line 2 in file2. See execution_table row 2 where difference is detected.

Why are some lines not shown in diff output?

Lines that are the same in both files are not shown to keep output clear. Only differences appear, as in rows 1 and 3 of execution_table.

Visual Quiz - 3 Questions

Look at the execution_table, what is the output after step 2?

A 1c1 < Hello world --- > Hello world

B 2c2 < This is line two --- > This is line 2

C No differences

D End of files

💡 Hint

Check the 'Output' column at step 2 in the execution_table.

At which step does diff detect a difference?

A Step 2

B Step 1

C Step 3

D Step 4

💡 Hint

Look at the 'Difference Detected' column in execution_table.

If file2.txt had the same content as file1.txt, what would the output be?

A Shows only first line difference

B Shows all lines as changed

C No output, files are identical

D Shows error message

💡 Hint

Refer to how diff only outputs differences, see variable_tracker 'output' when no differences.

Concept Snapshot

diff command compares two files line by line
Shows differences with line numbers and symbols
'c' means changed, 'a' added, 'd' deleted
Only differing lines are shown
Useful for quick file comparison in terminal

Full Transcript

The diff command compares two files by reading them line by line. It checks if each line matches or differs. When a difference is found, diff outputs the line numbers and the differing lines with symbols like 'c' for changed. Lines that are the same are not shown. This helps users quickly see what changed between two files. For example, if line 2 differs, diff shows '2c2' and the differing lines from each file. The process continues until all lines are checked or files end. If files are identical, diff outputs nothing.